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2011 Super Outbreak Hypothetical
This article covers a hypothetical scenario for the 2011 Super Outbreak in which the afternoon MCS never formed. This is to explore how the environment would change, and how extensive the outbreak could've potentially been had this one thing not been a factor. The 2011 Super Outbreak was the largest, costliest, and deadliest tornado outbreak ever recorded, taking place along the Southern, Midwestern, and Northeastern United States while inflicting catastrophic damage in the process. The event overall impacted 22 states, producing numerous violent, deadly, and destructive tornadoes throughout the affected regions. In all, 453 tornadoes were confirmed by NOAA's National Weather Service (NWS) and Government of Canada's Environment Canada across the 22 states and one Canadian Province. Widespread and destructive tornadoes occurred on each day of the outbreak, with April 27th being the most prolific and violent day with 309 tornadoes occuring within a 24 hour period from midnight to midnight CDT (0500 - 0500 UTC). Nine of the tornadoes were destructive enough to be rated EF5 with 27 more being rated EF4, thus making the outbreak the most violent on record, far surpassing the 1974 outbreak for the position. In total, ____ people were killed as a result of the outbreak, which includes ____ tornado-related deaths across 10 states and an additional ____ fatalities caused by other storm related events such as straight-line winds, hail, flash flooding, or lightning. In _____ alone, _____ tornado-related fatalaties were confirmed by the Storm Prediction Center (SPC) and the state's Emergency Management Agency. April 27's ____ fatalities are the most on record in the United States in a single day, surpassing the number of fatalities inflicted on March 25, 1925 due to the Tri-State outbreak where at least 747 people were killed. Over 650 local storm reports were recieved for tornadoes over 4 days, indluding 387 in 17 states on April 27 alone. This event was the costliest tornado outbreak and one of the costliest natural disasters in United States history (even after adjustments for inflation), with total damages of approximately $__ Billion (2011 USD). Meteorological Synopsis The outbreak was a result of a vigorous upper level trough that cut into the Southern US on April 25. An extratropical cyclone developed ahead of this upper-level trough between northeastern Oklahoma and western Missour, and moved northeastward. Conditions were markedly similar on April 26, with a much higher and more focused threat of supercell storms along a corridor stretching from the Arkansas/Louisiana border and into southeast Texas. The SPC issued a High Risk for strong to violent long-track tornadoes in this region as mixed-layer CAPE values were expected to be around 3000-4000 J/kg while being intersected by a stationary boundary with enhanced SRH values across the open warm sector. The storm mode on April 26 was predicted to be largely discrete supercells at first, transitioning into a QLCS in the evening and overnight, with an increased damaging wind threat alongside embedded tornadoes. As the system moved eastward toward the Ohio, Mississippi, and Tennessee Valleys on April 27, a very powerful 80-100 knot mid-level jet intersected a vast warm sector that was present across the Valleys. This created extreme levels of wind shear, along with a new low pressure center developing towards the west and moving quickly northeastward from ArkLaTex into the Mississippi and Tennessee Valleys. This system, combined with the parent system to the northeast, generated a vast and powerful low-level jet that exceed 60 kts across the warm sector. This resulted in extreme theta-E advection from the Gulf, building in dewpoints as high as the low 80s in the Deep South an mid 70s as far north as Ohio. This, on top of dry and cool air advection overtop the warm sector thanks to the 700mb flow resulted in steep lapse rates an bountiful CAPE for supercell storms. In the south, mixed-layer CAPE exceeded 4000 J/kg, with nearly 3500 J/kg developing in the Ohio River Valley. All this, combined with temperatures ranging from the low 80s°F (around 30°C to the mid 90s°F (around 35°C), and helicity levels ranging from 450-650 m2/s2, the SPC highlighted an extreme risk for violent, long-track, deadly and destructive tornadoes. A total of 62 severe weather watches were issued by the SPC over the four day outbreak. This included 47 tornado watches--16 of which were Particularly Dangerous Situation (PDS) watches--and 15 severe thunderstorm watches. The SPC assigns numbers to each severe weather watch issued starting at the beginning of each year; however the SPC unsuccessfully used two of their allocated watch numbers during this outbreak (208 and 209) due to how busy things were. April 25 A large area of possible severe storms for April 25–27 was forecast as the Storm Prediction Center (SPC) issued a moderate risk of severe weather for three consecutive days, centered over Arkansas through Tennessee. At 3:25 p.m. CDT (2025 UTC), the SPC issued a Particularly Dangerous Situation (PDS) tornado watch for much of Arkansas and parts of Missouri, Oklahoma, Texas, and Louisiana. By the evening hours of April 25, tornadoes had been reported across a few states, some of which caused significant damage in Arkansas. An intense supercell thunderstorm tracked near the Little Rock area and a tornado emergency was declared for the city of Vilonia. A large EF2 wedge tornado struck the town, subsequently causing severe damage and killing four people. A strong EF3 tornado had also struck the Hot Springs Village area earlier that evening; that tornado caused severe damage and resulted in one death. Later that evening, another EF2 tornado caused extensive damage to both a school building and Little Rock Air Force Base as well. Severe flooding continued across a large area from the Red River valley to the Great Lakes. A total of 42 tornadoes and five tornado-related deaths were confirmed on the 25th. April 26 A high risk of severe weather was issued for April 26 for portions of Louisiana, Arkansas, Oklahoma, and Texas along and near the Interstate 30 corridor as conditions became even more favorable for extreme weather. A large PDS tornado watch with very high possibilities for tornadoes was issued for that same area that afternoon. Widespread tornado warnings were then issued in that area later that evening. An upper-level negatively-tilted trough with two embedded shortwaves generated two surface lows that propagated generally east. One of the surface lows tracked northeast along the Mississippi River into Wisconsin as it occluded. Tornado watches were issued for the Lower Great Lakes during the afternoon hours as supercell thunderstorms developed along the warm front lifting north across central Michigan. Two tornadoes touched down in Michigan and caused damage to farm structures. Further east, severe thunderstorms caused scattered wind damage and large hail across Pennsylvania and New York. Two-inch-diameter hail was reported in Lock Haven, Pennsylvania. An isolated supercell moved across Central New York throughout much of the afternoon, producing golf ball-sized hail in Syracuse and spawning a very brief EF1 tornado in Verona Mills, which primarily caused damage to trees. Another tornado — this one being in Gilbertsville — caused significant damage to a school's athletic field. The second surface low corresponded to an area of strong upper level divergence ahead of the downstream shortwave. As the low formed across Texas and deepened while moving east, a tightening pressure gradient force further strengthened the low-level jet, therefore creating a broad warm sector across the southeastern states. This also generated stronger wind shear, providing better organization for the supercell storms as a result. Numerous tornadoes touched down across several states, including Texas, Louisiana, Arkansas. Most of those tornadoes were weak, but a few of them caused considerable damage. A long-tracked wedge tornado caused EF2 damage in rural portions of Texas and Louisiana. An EF3 tornado destroyed structures and caused severe damage at Fort Campbell, Kentucky as well. A total of 55 tornadoes were confirmed the 26th, although no fatalities occurred. April 27 Very significant severe weather was ongoing early on April 27, though it quickly moved out of the area by sunrise. For the second day in a row, the SPC issued a High Risk of severe weather for the United States. Later that morning, the SPC even increased the probability for tornadoes to 45% along a region stretching from Meridian, Mississippi to Nashville, Tennessee, an extremely rare issuance exceeding high risk standards. Conditions were becoming increasingly favorable for violent tornado as the outbreak progressed. 'Morning Quasai-linear Convective System' During the early morning hours, a cold front with several embedded low pressure areas extended from east Texas northeastward into the Ohio River Valley. An upper-level disturbance that had moved accross the frontal boundary the previous evening sparked the development of a QLCS, or Quasai-linear Convective System. These are known for their ability to produce numerous tornadoes, especially significant ones. This storm system raced through Mississippi and Alabama at nearly 80 MPH, producing significant damaging winds and dozens of tornadoes, though most of them were weak. Several of them were strong, however, where an EF3 tornado caused major damage to homes in Coaling, Alabama, an EF2 and an EF3 tornado produced severe damage and a fatality near Eupora, Mississippi. Another EF3 tornado resulted in heavy damage in downtown Cordova, Alabama, which was struck by a violent EF4 tornado later that afternoon. One embedded cell that began in Cullman County, Alabama produced a long-tracked EF2 tornado that struck the town of Hanceville, killing one person. That cell would then produce over ten tornadoes (most rated EF1) to the northeast in Marshall County and another EF1 tornado in Dade County, Georgia. The initial storms caused widespread power and telephone line outages across Alabama and Tennessee. This line of storms also caused some NOAA weather radio transmitter sites to stop functioning for the remainder of the outbreak. Because of this, more than one million customers were without power and had no warning of any approaching tornadoes later that day. 'Afternoon Supercells' Category:Super Outbreaks Category:Violent Outbreaks Category:Deadly Outbreaks Category:Destructive Outbreaks Category:Alabama Tornadoes Category:Mississippi Tornadoes Category:Tennessee Tornadoes Category:Eastern United States Outbreaks Category:Southeastern Outbreaks Category:Midwestern Outbreaks Category:Northeastern Outbreaks Category:Georgia Tornadoes Category:Kentucky Tornadoes Category:Louisiana Tornadoes Category:Ohio Tornadoes Category:Pennsylvania Tornadoes Category:New York Tornadoes Category:Texas Tornadoes Category:Arkansas Tornadoes Category:Missouri Tornadoes Category:Oklahoma Tornadoes